Flame-retardant plastic composition, yarn and textile structure coated therewith

ABSTRACT

A halogen-free flame retardant plastic composition, for coating a substrate, comprising an acrylic resin and an intumescent agent. It is in the form of plastisol, and comprises therefore a plasticizing medium wherein the acrylic resin and the intumescent agent are dispersed, said plastisol being formulated such that, in combination: the viscosity remains not more than 6000 mPa&#39;s, measured with a Brookfiled RVT viscometer at 20 revolutions per minute, its rheological behaviour is pseudo-plastic and Newtonian.

This is a Divisional of application Ser. No. 11/798,603, which is a Continuation of application Ser. No. 09/936,923 filed Dec. 3, 2001, which in turn is a U.S. National Phase of Application No. PCT/FR00/00738, filed Mar. 23, 2000, which claims priority to French Patent Application Nos. 99 04202, filed on Mar. 30, 1999 and 99 03764, filed on Mar. 23, 1999. The disclosure of the prior applications is hereby incorporated by reference herein in their entirety.

The present invention relates to a halogen-free flame-retarded composition intended for coating a substrate, for example yarns or textile structures, in order to meet all particular specifications or applications, for example for the manufacture of sun screens such as blinds or curtains. More specifically, the invention relates to a flame-retarded composition, in the plastisol state, comprising a plasticizing medium, at least one acrylic resin, dispersed in said plasticizing medium, and an intumescent agent.

It is generally already known that there are composite yarns, which the Applicant manufactures and sells, comprising:

-   -   a core comprising a continuous yarn, especially made of an         inorganic material, for example glass;     -   a sheath or jacket comprising a matrix consisting of at least         one chloropolymer material, for example a polyvinyl chloride         (PVC);     -   a flame-retarding mineral filler incorporated into and         distributed in said matrix; and     -   a plasticizer.

Preferably, but not exclusively, such a yarn is obtained by coating the core with a plastisol comprising the chloropolymer material, for example PVC, and the plasticizer, and then by gelling the plastisol around the core.

Moreover, the Applicant has disclosed a halogen-free flame-retarded plastic composition, described in document FR-A-2 755 973, applicable to a substrate, such as a yarn made of a mineral or organic material, of natural or synthetic origin, such as glass, polyester, polyamide, polypropylene, polyethylene, and containing no halogen or halogenated compound. This flame-retarded plastic composition includes a binding fraction, which binds said composition, and an intumescent agent consisting at least of a strong-acid compound, which is thermally degradable, and a polyhydric carbon compound. Said binding fraction as such has a limiting oxygen index (LOI) at least equal to 25% and the intumescent agent essentially consists of said strong-acid compound and said polyhydric carbon compound, the solids content of the composition having a weight ratio of said strong-acid compound to said polyhydric carbon compound of between 1.5 and 2, and preferably of 1.85.

The flamed-retarded composition described may be in solid, molten or liquid form. Preferably, this composition is in the form of an aqueous dispersion.

Specialty fabrics obtained from yarns as described above, and when they are used in various environments, especially for furnishing both the interior and exterior of buildings or constructions, for example as blinds, are subject to fire behavior requirements defined by national or international homologation or authorization regulations and/or procedures.

Thus, the regulations applicable to such fabrics in the Federal Republic of Germany define various classifications characterized especially by the length of the specimen destroyed by the fire and by the temperature of the combustion smoke, these classifications being identified by the letters B1 to B3, the letter B1 characterizing the best fire behavior achievable by a material comprising organic materials.

As regards the regulations applicable in France, these also define various classifications characterized, on the one hand, especially by smoke emission and identified by the letters F0 to F5, F3 being the best behavior achievable by a material containing a halogenated polymer, and characterized, on the other hand, especially by the ignition time of the fabric and identified by the letters M0 to M4, the letter M1 identifying the best fire behavior generally achievable by a material comprising organic materials.

For the purposes of meeting the requirements in terms of fire behavior, it is known to incorporate into any plastic composition a suitable intumescent agent, formulated with the resin so as to achieve the required level of flame retardation.

With regard to coating a substrate, and in particular the core of a yarn, with a flame-retarded plastic composition, comprising an acrylic resin and an intumescent agent, the Applicant has sought the most appropriate coating method, that is to say a method capable of preserving, at the end, the properties of the yarn or of the composite structure obtained, in terms of heat-sealability and resistance to both high and low temperatures.

With regard to a yarn, the Applicant has firstly adopted, for this purpose, a coating method in which the core is passed through a die, with peripheral delivery around the core of a sheath of the flame-retarded plastic composition, in the ungelled plastisol state, that is to say with a plasticizing medium in which both the acrylic resin and the intumescent agent are distributed.

This way of applying the flame-retarded plastic composition to the substrate, that is to say in the plastisol state, avoids having to melt the resin, at a high temperature, which might degrade the final properties of the latter and degrade the intumescent agent.

Next, the Applicant sought optimal rheological properties of the flame-retarded compositions according to the invention, compatible with the coating processes using dies with a high shear rate (for example of the order of at least 15 000 to 20 000 s⁻¹ or even 100 000 s⁻¹).

According to the invention, this compatibility is obtained when the plastisol exhibits, at low shear rates, for example less than 300-400 s [sic], Newtonian-type behavior with a viscosity of less than or equal to 6000 mPa.s, measured using a Brookfield RVT viscometer at 20 revolutions per minute, and, at high shear rates, for example greater than 10 000 s⁻¹, pseudoplastic-type behavior.

As a person skilled in rheology knows, Newtonian behavior is characterized by a shear stress which varies linearly with shear rate and pseudoplastic behavior is characterized by a shear stress which reaches a limiting value when the shear rate increases.

In the case of the present invention, Newtonian behavior is revealed when it is possible to measure the viscosity of the flame-retarded composition using any suitable method, whether standardized or not, and pseudoplastic behavior is revealed by the ability of the flame-retarded composition to pass, without flow, through a coating die with a high shear rate, for example of the order of 15 000 to 20 000 s⁻¹.

Preferably, so as to preserve the properties of the composite yarn obtained, especially its heat-sealability and its weatherability, the weight proportion of the plasticizing medium comprising a phosphate is at most equal to 200% with respect to the weight of acrylic resin and/or the weight proportion of the intumescent agent is at most equal to 200% with respect to the weight of acrylic resin.

The plasticizing medium comprises predominantly, by weight, an organic phosphate, possibly and preferably with a phthalate.

The proportion by weight of intumescent agent is between 50 and 200%, and preferably between 150 and 200%, by weight of resin.

Any composite yarn or any composite textile structure, capable of being obtained by coating and then gelling a flame-retarded composition as defined above may achieve a fire resistance according to French Standard NFP 92503, especially classification level M1, and also good weatherability, meeting the ISO 105 standard, and finally good heat-sealability.

In the description and claims, the terms and expressions indicated below have the following meanings:

-   -   an “acrylic resin” is any synthetic polymer derived from         propenoic acid;     -   “a thermally degradable strong-acid compound” is a compound         which releases a strong acid either by itself or in situ from a         precursor, at high temperature, that is to say at between about         100° C. and about 250° C.;     -   “a polyhydric carbon compound” is a compound generally chosen         from the various classes of carbohydrates and having a         relatively high amount of carbon and many hydroxyl sites;     -   “a liquid phosphorus derivative” is a flame-retarding product         which comprises phosphate groups and is in liquid form;     -   “a gas-generating agent” is a product which, by thermal         degradation due to the effect of temperature, releases a gas,         for example carbon dioxide or ammonia;     -   “a plastisol in the gelled state” is a dispersion of polymers,         fillers and various additives in a plasticizer.

In another preferred embodiment according to the invention, the flame-retarded plastic composition also comprises a phosphate-type plasticizer. With a phosphate/phthalate-type plasticizer, the performance is better, in terms of low viscosity, and there is less plasticizer exudation after gelling.

As examples of phthalate-type plasticizers, mention may be made of the plasticizers PALATINOL C and PALATINOL N available from BASF.

As phosphate-type plasticizers, mention may be made of DISFLAMOLL DPO and DPK® available from Bayer.

As examples of phosphate/phthalate-type plasticizers, mention may be made of those available from Solutia.

In yet another preferred embodiment according to the invention, the acrylic resin is a homopolymer or copolymer based on methyl methacrylate.

Such a resin may, for example, be chosen from the resins BM 310® and BM 410® available from Rohm.

The flame-retarded plastic composition according to the invention may also include UV stabilizers and/or opacifiers and/or pigments and/or viscosity-reducing processing aids.

As UV stabilizers, mention may especially be made of compounds of the benzophenone type, such as TINUVIN P available from Witco, or compounds of the benzotriazole type, such as TINUVIN 320 available from Witco or LOWILITE 55 available from Great Lakes.

As opacifiers, mention may especially be made of calcium carbonates and zinc sulfides.

As pigments, mention may especially be made of products from the IRGALITHE or CHROMOPHTAL ranges available from Ciba-Geigy.

As viscosity-reducing processing aids, mention may especially be made of the viscosity reducers available from Byk Chemie.

The intumescent agent of the composition according to the invention therefore comprises at least one strong-acid compound.

Preferably, the thermally degradable strong-acid compound is chosen from the group consisting of phosphoric acids, boric acids, and salts of these acids with a volatile cation, and preferably ammonium polyphosphate. This is because the acid source agent is chosen to be able to dehydrate, effectively, the carbon source agent, if it is present, above a certain temperature or in the presence of a flame, and to release the acid in temperature ranges close to the ignition temperature of the substrate to be flame-retarded.

The intumescent agent may also comprise a polyhydric carbon compound. The polyhydric carbon compound is preferably a starch or a polyhydric alcohol, and more preferably pentaerythritol. This is because these agents contain a relatively high amount of carbon and have many hydroxyl sites, thereby favoring the formation of a highly expanded residue.

The intumescent agent may also comprise liquid phosphorus derivatives which make it possible to further reduce the viscosity of the fluid plastisol. These derivatives are preferably chosen from products of the FYROL® range available from Akzo.

The intumescent agent may also comprise gas-generating agents such as, in particular, melamine.

In a highly preferred embodiment according to the invention, the flame-retarded plastic composition comprises, by weight:

acrylic resin 100.00 parts phosphate/phthalate plasticizers 125.00 parts liquid phosphorus derivatives 5.00 parts ammonium polyphosphate and melamine 97.50 parts 50/50 pentaerythritol/melamine 52.00 parts

Another subject of the invention is a flame-retarded composite yarn comprising a core of low combustibility, made of a mineral or organic material, for example a halogen-free material, and a sheath made of a plastic capable of being obtained from the flame-retarded composition as defined above. The material of the core is, for example, a continuous glass filament.

The core made of halogen-free material of the composite yarn according to the invention may be chosen from the group consisting of a yarn made of a mineral or organic material, of natural or synthetic origin, such as glass, glass filament, polyester, polyamide, polypropylene and polyethylene. Preferably, a core made of a glass yarn or a continuous glass fiber, or filament, will be chosen.

The subject of the invention is also a textile structure in which the composite yarns as obtained above are assembled or entangled.

Another subject of the invention is a substrate of low combustibility, for example a textile structure, coated with a resin layer, obtained by coating and then gelling a flame-retarded composition as defined above.

Further subjects according to the invention are, respectively, a sun screen, a sign, and a covering for walls or ceilings, comprising a textile structure as defined above.

The examples which follow illustrate the invention but do not in any way limit the scope of the appended claims.

EXAMPLE 1 Formulation I of a Fire-Retarded Plastic Composition

-   -   Plastisol:

Acrylic resin (BM 310 from Röhm) 100.00 parts Phosphate/phthalate plasticizer 125.00 parts

-   -   Intumescent agent:

Ammonium polyphosphate 120.00 parts  Pentaerythritol 31.00 parts Melamine 31.00 parts

-   -   Lubricant:

Silicone oil 2.50 parts

Such a fire-retarded plastic composition has, in its Newtonian range, a viscosity of 4600 mPa.s measured using a Brookfield RVT viscometer at 20 revolutions per minute. Moreover, at high shear rates, it is pseudoplastic.

The fire behavior tests were carried out on glass fabrics coated with the fire-retarded plastic composition described above, as well as on composite yarns formed from about 54% (or 50%) of continuous glass filament and from 46% (or 50%) of the fire-retarded plastic composition described above.

The results of the tests carried out demonstrate that the M1 classification of the NFP 92503 Standard can be assigned to the textiles thus obtained.

EXAMPLE 2 Formulation II of a Flame-Retarded Plastic Composition

-   -   Plastisol:

Acrylic resin (BM 310) from Röhm 100.00 parts Phosphate/phthalate plasticizer 125.00 parts

-   -   Intumescent agent:

Ammonium polyphosphate 38.00 parts Pentaerythritol 31.00 parts BUDIT 3077B fire-retarded system 150.00 parts  (available from Budenheim)

-   -   Lubricant:

Silicone oil 2.50 parts

Such a fire-retarded plastic composition has, in its Newtonian range, a viscosity of 6000 mPa.s measured using a Brookfield RVT viscometer at 20 revolutions per minute. Moreover, at high shear rates, it is pseudoplastic.

The same tests as those described in Example 1 were repeated, giving the same results.

EXAMPLE 3 Formulation III of a Flame-Retarded Plastic Composition

-   -   Plastisol:

Acrylic resin (BM 310) from Röhm 80.00 parts Acrylic resin (VP 8744) from Röhm 20.00 parts Phosphate/phthalate plasticizer 130.00 parts 

-   -   Intumescent system:

Ammonium polyphosphate 115.00 parts  Pentaerythritol 31.00 parts Melamine 31.00 parts Liquid phosphorus derivative  5.00 parts

-   -   Lubricant:

Silicone oil 2.50 parts Wetting agent 5.00 parts

Such a fire-retarded plastic composition has, in its Newtonian range, a viscosity of 4300 mPa.s measured using a Brookfield RVT viscometer at 20 revolutions per minute. Moreover, at high shear rates, it is pseudoplastic.

The same tests as those described in Example 1 were repeated, giving the same results.

EXAMPLE 4 Formulation IV of a Fire-Retarded Plastic Composition

-   -   Plastisol:

Acrylic resin (BM 310) from Röhm 80.00 parts Acrylic resin (VP 8744) from Röhm 20.00 parts Phosphate plasticizer 130.00 parts 

-   -   Intumescent system:

Ammonium polyphosphate 115.00 parts  Pentaerythritol 31.00 parts Melamine 31.00 parts

-   -   Lubricant:

Silicone oil 2.50 parts

Such a fire-retarded plastic composition has, in its Newtonian range, a viscosity of 5250 mPa.s measured using a Brookfield RVT viscometer at 20 revolutions per minute. Moreover, at high shear rates, it is pseudoplastic.

The same tests as those described in Example 1 were repeated, giving the same results.

Many other fire-retarded plastic compositions may be formulated and qualified by routine tests, based on the above examples, and on the following supplementary considerations:

1) the final rheological behavior depends largely on the plasticizer used, more specifically on its chemical nature and its proportion; in this regard, a plasticizer comprising a phthalate must be preferred;

2) the proportion of the components or compounds in the intumescent agent has little effect on the final rheological behavior, since in particular the actual intumescent properties are desirable; in contrast, the proportion of the intumescent agent is important with regard to the final rheological behavior. This proportion must be limited, otherwise it will impair the fire retardancy;

3) any viscosity-reducing additive allows these rheological properties to be adjusted, if necessary. 

1. Method for obtaining a yarn comprising a core and a plastic sheath comprising an halogen-free flame-retarded composition, containing at least one acrylic resin and an intumescent agent which are dispersed in a plasticizing medium, the method comprising: a) providing a die suitable for passing the core of said yarn therethrough; b) ungelling the plastic composition to be in a plastisol state; c) passing the core of the yarn through said die, with a peripheral distribution of said plastisol around said core; d) gelling the fire-retarded composition, wherein the rheological properties of the plastisol at the shear rate of the die, at least equal to 20,000 s⁻¹, are adapted by formulating said ungelled plastisol so that at low shear rate, at most equal to 400 s⁻¹, it exhibits a Newtonian behaviour, with a viscosity of less than or equal to 6 000 mPa.s, measured with a Brookfield RVT viscometer at 20 rpm, and at high shear rate, at least equal to 10,000 mPa.s, it exhibits a pseudoplastic behaviour.
 2. The method according to claim 1, wherein the plasticizing medium contains an organic phosphate as the major component by weight in said plasticizing medium and a phthalate.
 3. The method according to claim 2, wherein a weight proportion of the plasticizing medium comprising the phosphate is at most equal to 200% with respect to the weight of acrylic resin and/or a weight proportion of the intumescent agent is at most equal to 200% with respect to the weight of acrylic resin.
 4. The method according to claim 1, wherein the proportion by weight of the plasticizing medium in the plastisol is between 100 and 200% by weight of resin.
 5. The method according to claim 1, wherein the proportion by weight of the plasticizing medium in the plastisol is between 120 and 145% by weight of resin.
 6. The method according to claim 1, wherein the proportion by weight of the intumescent agent in the plastisol is between 50 and 200% by weight of resin.
 7. The method according to claim 1, wherein the proportion by weight of the intumescent agent in the plastisol is between 150 and 200% by weight of resin.
 8. The method according to claim 1, wherein the core material is a continuous glass filament.
 9. A composite flame retardant yarn with a sheath of resin of low combustibility obtained by the method according to claim
 1. 10. The yarn according to claim 9, wherein the core material is a continuous glass filament.
 11. A textile structure in which yarns as claimed in claim 9 are assembled or entangled.
 12. A sun screen comprising a textile structure as claimed in claim
 11. 13. A sign comprising a textile structure as claimed in claim
 11. 14. A covering for walls or ceilings, comprising a textile structure as claimed in claim
 11. 